The present invention relates to a fuel supply device for an internal combustion engine.
Fuel supply devices of this type are disclosed for example in the publication xe2x80x9cDieselmotor Managementxe2x80x9d, Verlag Vieweg, 2 edition 1999, pages 262-263. The fuel supply device has a feed pump which supplies the fuel from a supply container to a high pressure pump. With the high pressure pump, the fuel is supplied under high pressure at least indirectly to injection points on the internal combustion engine. The feed pump is driven mechanically by the internal combustion engine. During start of the internal combustion engine the feed pump is driven with a low rotary speed, so that the fuel quantity supplied by it in this condition is not sufficient to provide a reliable start of the internal combustion engine. In particular, at high fuel temperatures and low rotary speeds of the internal combustion engine, for example because of a not sufficient voltage of the board current source, the feed pump does not supply sufficient fuel quantity. The feed pump can be modified so that it supplies a greater fuel quantity, but in other operational conditions then the required fuel quantity will be too high and must be uselessly withdrawn.
Accordingly, it is an object of the present invention to provide a fuel supply device for an internal combustion engine, which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a fuel supply device for an internal combustion engine which has a supply container, at least one feed pump for supplying a fuel from the supply container, a high pressure pump to which the fuel is supplied from the supply container by the feed pump, so that the fuel is supplied under high pressure at least indirectly to injection points of an internal combustion engine, the feed pump being driven mechanically by the internal combustion engine, and a further feed pump provided additionally to the mechanically driven feed pump and supplying the fuel from the supply container to the high pressure pump, the further feed pump having an electric drive and being operable independently from the mechanically driven feed pump.
When the fuel supply device is designed in accordance with the present invention, it has the advantage that by the electrically driven further feed pump, intentionally in the required operational conditions the fuel quantity supply by the high pressure pump is increased, so that a reliable start and a reliable operation of the internal combustion engine is guaranteed in all operational conditions.
In accordance with another feature of present invention, the mechanically driven feed pump and the further feed pump are assembled to form a feed module. Therefore a simple construction is provided.
In accordance with a further feature of present invention, the feed module has a suction connection to the supply container, through which both feed pumps aspirate fuel, a pressure connection to the high pressure pump through which both feed pumps supply fuel, and a check valve arranged between the pressure connection and the further feed pump and closing toward the further feed pump. With this construction a return flow of the fuel, which is supplied by the mechanically driven feed pump through the further feed pump into the supply container, is reliably prevented.
In accordance with another feature of present invention, the further feed pump is operated in the event of a failure of the mechanically driven feed pump. Therefore it is guaranteed that the internal combustion engine at least in an emergency situation can operate in the case of a failure of the mechanically driven feed pump.
Finally, in accordance with another feature of present invention, the further feed pump supplies a smaller fuel quantity than the maximum fuel quantity of the mechanically driven feed pump. Therefore a simple and cost favorable construction of both feed pumps can be provided.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.